The subject matter of this application relates to systems and methods that provide optical signals over a cable transmission network.
Early CATV systems were configured to deliver content along a coaxial transmission path from a content provider to its subscribers. As these systems evolved to not only provide a greater amount of content, but to provide data services that travel to and from the subscriber (e.g. Internet service), much of the coaxial path from the provider to the subscribers was replaced with fiber-optic cable, which could transmit a signal over a greater distance with less intermediate amplification. Such systems are typically referred to as hybrid-fiber coax (HFC) systems because the majority of the transmission between a head end that sends a signal and a customer that receives a signal is propagated along optical fiber, except for the short distances proximate the customers' premises, which is coaxial.
Fiber optic communication systems offer many advantages, including high data transfer rates and substantial immunity to electromagnetic interference. Networks that can integrate fiber optics for data transfer, such as cable television (CATV) networks, can increase performance for the consumer. However, it is generally expensive to lay fiber optic cable, especially in dense metropolitan areas. This has led to increasing demands for higher data rates on existing fiber, and attempts to send light down longer stretches of fiber. Technologies for increasing the data rate of fiber optic communication include Course Wave Division Multiplexing (CWDM) and Dense Wave Division Multiplexing (DWDM).
A typical optical system may operate with cable television (CATV) RF carrier frequencies, such as National Television System Committee (NTSC) RF carrier frequencies. In an optical link that is transporting many radio frequency (RF) carrier channels, there exists composite second order distortion (CSO) components. The CSO components result from inherent nonlinearity of the link components, laser chirp interactions, dispersion along the fiber, and other effects. CSO degrades performance of the CATV network and therefore, improved techniques for reducing CSO distortions in a CATV network are desirable.